leonardo painted on wood. the background on the younger mona lisa, is, well, muddy, not like the masterpiece. >> it adds up to being an interesting copy. >> reporter: an interesting copy? >> reporter: there are many reasons to believe this is a copy by a lesser artist. first, the younger painting is on canvas. leonardo painted on wood. the ground on the younger mona lisa is, well, muddy, not like the masterpiece. but the real give away, translucence. in the original, layers of light. they're just not there in the other one. >> you go, wow. you look at that mona lisa and you go -- ah. >> reporter: a new leonardo would be worth at least $100 million. but imagine, with only about 20 of his works in existence, how exciting it would be to discover 1 more. jeffrey kofman, abc news, oxford. >> neat to think about. well, that's what's making news in america this morning. >> stay with us for "good morning america." have a great friday.